Delta-shaped aircraft are characterized by highly swept-back wings and a relatively low aspect ratio which results in a generally triangular planform. While conventionally shaped aircraft are defined by a central fuselage with laterally protruding wings, delta-shaped aircraft have an integrated fuselage and wing configuration. In this respect, typically the modern "stealthy" type of delta-shaped aircraft have an aerodynamic lifting surface which is defined by a central fuselage which smoothly blends with highly swept-back wings. In fact, because of this smooth integration, these aircraft are contemplated as having only a single wing and these aircraft are sometimes referred as being a "flying wing." Some present examples of delta-shaped aircraft include the U.S. military's B-2 bomber and the F-117 stealth fighter.
When designing a low radar observable aircraft it is desirable to align the leading edges of the aircraft when observed in the plan view, i.e., topwise or bottomwise. This tends to "group" together detected radar spikes such that the spikes occur at fewer discrete angles, and provides lower off-spike signatures. It is further desirable to maintain long edges in order to provide as narrow an edge spike as possible. This design methodology is known as "spike and fuzzball," and results in radar signatures that are characterized by a few large narrow spikes at specific viewing angles combined with a "noisy" low magnitude "fuzzball" signature elsewhere.
It is further desirable to align the leading edges of the aircraft wings in a common horizontal plane. Where the leading edges are not aligned in the horizontal plane, the detected radar spikes from these leading edges tend to appear less and less aligned as the aircraft is observed from greater and greater elevation angles. This effect is known as "spike walk", and arises due to purely geometrical considerations. As such, as one of ordinary skill in the art can appreciate, the failure to align the leading edges in the horizontal plane may increase the aircraft deflectability at non-zero elevation angles from both a spike and fuzzball perspective.
As one of ordinary skill in the art will further appreciate, aircraft must typically reduce their speed when performing landing operations. To perform this function, conventional aircraft typically employ flaps which are rotably attached to the trailing edges of the wings. The flaps are deflected downward, and in some configurations the flaps are also extended afterward, in order to produce drag, thereby slowing down the aircraft to required landing flight speeds.
The modern stealthy delta-aircraft as described above, however, do not have traditional flaps at the trailing edges of the wings. For example, in the case of the B-2 stealth bomber, the aircraft does not even have downwardly deflectable or afterward extendable flaps for producing drag and slowing the aircraft. These aircraft typically have angled elevons and rudders for their control surfaces which are mounted to the trailing edge of the wing. Among other design constraints, this is primarily due to radar signature mitigation reasons and the inability to balance the resulting pitching moments. As such, in addition to reducing engine power, these aircraft reduce their speed for landing operations by approaching the landing area at a relatively high angle-of-attack or nose-up in order to increase drag.
As one of ordinary skill in the art can appreciate, the operation of an aircraft at a high angle-of-attack negatively impacts the directional stability. This is inherently problematic for delta-shaped aircraft designs due to their geometry. In order to achieve directional stability, however, the design of delta-shaped aircraft typically must use aerodynamic control surfaces, even at the undesirable cost of increasing the radar observable signature of the aircraft. Such control surfaces may include, for example, tail fins and rudders.
As such, based upon the foregoing, there exists a need in the art for an improved method and device, for use with a delta-shaped aircraft which improves directional stability without substantially interfering with the aircraft aerodynamic and radar detectability characteristics in comparison to the prior art.